I'm going to pay the same way I was going to with one modification:
Terra: Finish Beginning sequence.
Switch.
Ven: Finish Beginning sequence.
Switch.
Aqua: Finish Beginning sequence.
Switch.
Terra: Finish first world.
Switch.
Ven: Finish first world.
Switch.
Aqua: Finish first world.
Switch.
Etc...
I was going to do the order: Aqua > Terra > Ven.
But this way works as well.
T. Nomura has said that it wouldn't be good to do that, because you would get really confused or something